CHARS_TO_REMOVE = '.,"\';:!()?[]'

def normalize_word(word):
    '''return a word lowercase and stripped of punctuation'''
    for char in CHARS_TO_REMOVE:
        word = word.replace(char, '')
    return word.lower()
    

def count_words(filename):
    '''returns a dictionary mapping words to the number
    of times the word appears in filename'''
    word_counts = {}
    file = open(filename)
    
    for line in file:
        line = line.strip() # throw away newline
        
        words = line.split() # get all the words in the line
        
        for word in words:
            word = normalize_word(word)
            word_counts[word] = word_counts.get(word, 0) + 1
            
    file.close()
    
    return word_counts